This is a very strange thing that happened just recently and only with some pieces of a clip:

I've pulled an interview clip with 2 audio tracks into the timeline.
One is the track of the person who gave the interview (1), the other one the track of the interviewer (2).
All was fine and I cut the clip up into several pieces that have to be dragged around in order to line them up thematically with pieces from other clips (other sessions).

But when I opened the file last time, two of the pieces suddenly had the content of track 1 in both tracks, so I have 2 identical audio pieces in 2 different tracks and the original content of track 2 is gone and has been replaced by a duplicate of the content of track 1.

I'm working with the AppImage of Kdenlive 21.12.0 on Ubuntu Mate 20.04.
The clips are .mkv files recorded with OBS Studio on Ubuntu Mate 20.04.

Does anyone have an idea what has happened there and, more importantly, how I can prevent that from happening to the other pieces and reverse it for the two that have been affected without searching for them in the source file to drag them down into the timeline again (because that would be VERY time-consuming)?

I also have a piece where I had only 1 audio track and the sound is suddenly gone from that track completely while the video is still in place but this one is easier to relocate.

The file has been saved and opened a few times before that happened and contains some 2,5 hours of material.